Modern computing and display technologies have facilitated the development of systems for so called “virtual reality” or “augmented reality” experiences, wherein digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user.
When placing digital content (e.g., 3-D content such as a virtual chandelier object presented to augment a real-world view of a room, or 2-D content such as a planar/flat virtual oil painting object presented to augment a real-world view of a room), design choices may be made to control behavior of the objects. For example, the 2-D oil painting object may be head-centric, in which case the object moves around along with the user's head (e.g., as in a Google Glass approach); or the object may be world-centric, in which case it may be presented as though it is part of the real world coordinate system, so that the user may move his head or eyes without moving the position of the object relative to the real world.
When placing virtual content into the augmented reality world presented with an augmented reality system, whether the object should be presented as world centric (i.e., the virtual object stays in position in the real world so that the user may move his body, head, eyes around it without changing its position relative to the real world objects surrounding it, such as a real world wall); body, or torso, centric, in which case a virtual element may be fixed relative to the user's torso, so that the user may move his head or eyes without moving the object, but such movement is slaved to torso movements; head centric, in which case the displayed object (and/or display itself) may be moved along with head movements, as described above in reference to Google Glass; or eye centric, as in a “foveated display” configuration wherein content is slewed around as a function of what the eye position is.
Some conventional approaches uses optical waveguides having surface relief type diffractive elements (e.g., linear gratings) to redirect light beams from an image source to provide pupil expansion and to produce virtual content display to an observer's eye (in a monocular arrangement) or eyes (in a binocular arrangement). These waveguides having surface-relief type diffractive elements require complex designs of digital diffractive patterns. These complex designs are subsequently converted into high resolution binary mask information and then exposed onto a reticle or transferred to an electronic-beam writing device (e.g., lithographic writing equipment). These digital diffractive patterns are then authored or printed into a photoresist material and subsequently etched using various etching techniques. Such surface relief type diffractive elements are not only costly to manufacture, but the resulting structures are also fragile and vulnerable to inadvertent damages or contamination due to the existence of microscopic relief structures.
Thus, there exists a need for methods and apparatus having enhanced diffractive elements for displaying virtual content for virtual or augmented reality.